This invention relates to a method and an apparatus for recording on and reproducing from a magnetic disk having its recording area divided into a plurality of sectors, each sector including an ID area and a data area, and more particularly to a method for recording on or reproducing from a magnetic disk, which method contributes to increasing the access speed.
This invention relates to a magnetic recording and reproducing apparatus for recording on a magnetic disk having a plurality of divided recording areas, each divided recording area including an identification area and a data area, and more particularly to a magnetic recording and reproducing apparatus, a control circuit for the magnetic recording and reproducing apparatus and a magnetic recording and reproducing method, which are most suitable for magnetic recording and reproduction with a dual head (hereafter referred to the dual head) combining a reproducing head, such as an MR (magneto-resistive effect) head and a recording head.
The bit error rate of data transferred from a magnetic disk unit to a computer is generally desired to be 1.0E-14 or less. However, it is virtually impossible to keep the bit error rate of data read from the magnetic disk at a level of this order. Therefore, normally, redundant bits for error check or error correction are added to record data, and a magnetic disk controller (hereafter referred to as the controller), provided between the magnetic disk unit and the computer, is used to detect or correct errors of data which is read by the controller so as to limit the bit error rate of data from the controller to the computer to 1.0E-14 or less even when the tolerance limit for the bit error rate of data from the magnetic disk unit is about 1.0E-9. Incidentally, in view of the error correction capability of the controller, it is possible to further tolerate the bit error rate of data read by the controller. If more errors can be tolerated in accordance with the difference between the current bit error rate and the deteriorate bit error rate, for example from the current 1.0E-9 to 1.0E-6, in compliance with an increase in the so-called window margin, the recording density, or the recording capacity of the magnetic disk can be increased. However, as the bit error rate is deteriorate, the greater number of times error bits are corrected. If the correction process time for one error is long, a large overhead for the error correction process causes the performance of the apparatus to deteriorate. Heretofore, there has been a problem that correcting errors takes time for the reason described below, and after all, the bit error rate of data read from the magnetic disk into the controller cannot be improved. Specifically, the magnetic disk is normally divided into a plurality of sectors for a more effective access. FIG. 2 shows a recording format for each of the sectors 1, 2, . . . . The sectors 1, 2, . . . are divided into the ID areas, ID0, ID1, ID2, . . . and the data areas DATA0, DATA1, DATA2, . . . . The data areas ID0, ID1, ID2, . . . are each divided into information PROSYNC for phase synchronization of a PLL (phase lock loop), AM indicating the leading end of the ID area, C for a cylinder number of data, H for a head number of data, S for a sector number of data, CRC indicating whether or not an error has occurred, and ID PAD indicating a border between the ID area and the data area. Recording or reproduction of the record format on a data area of the magnetic disk is executed after information of the ID area of the same sector is verified. Error detection of the ID information is performed by comparing an error check code generated by using the ID information which has been read and an error check code CRC recorded in advance. This error detection can be done at high speed, but if an error is detected, data has to be read again (by retry), for which a waiting time for one rotation of the disk is required. In order to solve this problem, it has been proposed to correct errors in the information of the ID area by adding an error correcting code to the ID area as disclosed in JP-A-63-86160 (Prior Art 1). However, the conventional method for error correction takes time. Unless the error correction of the ID area is finished by the time data is written in the data area specified by the ID, a disk rotational delay occurs. To avoid this problem, there has been proposed a method for placing the corresponding ID areas and data areas in different sectors instead of placing in the same sectors to thereby secure time for correcting errors, as shown in FIGS. 3A to 3D.
In the past, magnetic heads, such as the inductive head or the MIG (Metal In Gap) head capable of both reading and writing, were used to read data from or write onto the magnetic disk unit.
Recently, dual heads, containing a magnetic head for writing (inductive, MIG, etc.) and a magnetic head for reading, are mounted. In addition, an MR (Magneto-Resistive) head, which is not dependent on the rotating speed of the disk and which is compatible with small disks, has began to be used for the magnetic head for reading.
The dual head as described has a problem that because it is generally manufactured in a monolithic body including the writing head and the reading head, a discordance occurs invariably between the core centers of he two heads in the manufacturing process.
According to a technique revealed in JP-A-3-160675, in the magnetic disk unit using a dual head, servo information is provided separately for writing and reading in the areas on the magnetic disk which are shifted with respect to each other by the amount equal to the distance of a radial shift between with the reading head and the writing head, and under this head configuration, data can be written into the data area without moving the magnetic head. (See FIG. 38.)
Though not disclosed in the above-mentioned patent publication, the format pattern that the inventors presumed from the description of the patent publication is shown in FIGS. 39A to 39C. Description will now be made of W.SPLICE. When writing data, it is confirmed by reading information in the ID area whether or not an object sector is accessed reading information of the ID area and the magnetic head unit writes data in the next area. It is necessary to gain time from this reading until the electronic circuit for writing becomes ready for operation. The area provided for gaining this time is W.SPLICE.